EFFECT OF INORGANIC ADDITIVES ON SOLUTIONS OF NONIONIC SURFACTANTS .15. EFFECT OF TRANSITION-METAL SALTS ON THE CLOUD POINT OF OCTOXYNOL-9 (TRITON X-100)

The salt effects of 10 transition metal cations on nonionic surfactant s were investigated by the action of their salts (nine nitrates, two s ulfates) on the cloud point (CP) of octoxynol 9. All cations investiga ted raised the CP of octoxynol 9 by complexation with its ether groups , which represents salting in, However, aside from Ag+, these CP incre ases were no larger than those caused by Li+ and by di-and trivalent c ations not belonging to the transition metal group, even though the tr ansition metal cations have a greater capacity for forming complexes. This unremarkable, average salting-in capacity of most transition meta l cations is attributed to competition for their coordination sites be tween the ether groups of the surfactant and water. With the exception of silver, the solid nitrates of all transition metals examined form stable solid hydrates containing three to nine molecules of water of c rystallization, which indicates a high affinity of the cations for wat er, Only AGNO(3) forms no stable solid hydrates. The Low affinity of A g+ for water results in a commensurately higher capacity for binding t he ether groups of the surfactant. This was shown by the facts that Ag NO3 produced the largest CP increases and that it was the only salt to reversibly precipitate an insoluble adduct with octoxynol 9 from conc entrated solutions, The only salt that oxidized the surfactant when it s solution was heated in a nitrogen atmosphere and illuminated during CP measurements was Fe(NO3)(3). Oxidative degradation produced small b ut progressive CP reductions. (C) 1997 Academic Press.